Comparison of the RF MEMS switches with dielectric layers on the bridge’s lower surface and on the transmission line

Previously, we proposed that the dielectric layer of RF MEMS switch can be fabricated either on the transmission line, as traditional switches, or on the lower surface of the bridge. This paper presents a detailed comparison of the RF MEMS switches with different positions of dielectric layer. Through theoretically analyzing the physical model of fringing capacitance, it is revealed that different positions of dielectric layer can result in different switch capacitances. Therefore, the change of dielectric-layer position can reduce the switch capacitance and insertion loss when the bridge is much wider than t-line. The theoretical analysis is demonstrated by Maxwell 3D and HFSS simulation, showing that the insertion loss is reduced by around 13% when the bridge width is three times of transmission line width. Further, the influence of switch’s structural parameters, such as dielectric material and dimensions of dielectric layer, on the differences between these two kinds of switches is discussed. To achieve high integration together with low-loss and low-actuation-voltage design, the novel switch with dielectric layer on bridge’s lower surface can be expected to have broad applications in the future.